In the field of this invention it is known in integrated circuits to produce an analogue trim value that is used to trim a reference voltage produced by the integrated circuit. It is highly desirable that this trim value is substantially independent of temperature variations, especially in automotive applications where large temperature ranges are specified.
It is known to provide analogue trim values using fuses, zener zaps and EEPROMs to provide digital trim information to trim a voltage. It is also known to use EEPROMs and resistors together to store analogue trim information. However, a problem with these arrangements is that although a voltage may be trimmed precisely at a given temperature, the nature of analogue signals means that this precision is not well maintained over a range of temperatures. For an integrated circuit used in an automotive application, the operable temperature range may typically be −40° C. to 125° C.
What is needed is an arrangement in which an analogue trim value is provided which is substantially temperature independent over such a temperature range. In other words, the trim value must have a negligible temperature coefficient.
It is an object of the present invention to provide an EEPROM circuit, a voltage reference circuit and a method for producing a low temperature-coefficient voltage reference wherein the abovementioned disadvantages may be alleviated.